Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $60.25   6.195%   $63.9825   $63.98   $64.00   $64.00  
  Purchase #2 $234.45   9.574%   $256.8962   $256.90   $256.90   $256.90  
  Purchase #3 $131.31   5.466%   $138.4874   $138.49   $138.50   $138.50  
  Purchase #4 $119.72   11.709%   $133.738   $133.74   $133.75   $133.70  
  Purchase #5 $143.85   13.873%   $163.8063   $163.81   $163.80   $163.80  
  Purchase #6 $229.45   4.588%   $239.9772   $239.98   $240.00   $240.00  
  Purchase #7 $115.45   5.755%   $122.0941   $122.09   $122.10   $122.10  
  7 purchase totals = $1,034.48       $1,118.9817   $1,118.99   $1,119.05   $1,119.00